This invention relates generally to the control of fluid being delivered from a pump and more specifically to a variable delivery control arrangement for a pump.
Variable delivery pumps are well known in the art. Various ones use an adjustable swash plate to control the movement of a plurality of pistons thus controlling the volume of fluid being delivered therefrom. Others use an adjustable sleeve arrangement disposed around each of the pistons that functions to selectively control the volume of fluid being expelled from each of the pumping chambers. These well known variable delivery pumps are effective to control the volume of fluid being delivered from the pump. The various control arrangements used to control the volume of fluid ranges from very simple to very complex. U.S. Pat. No. 5,515,829 which issued to James R. Blass et al. on May 14, 1996 teaches a more complicated direct acting control arrangement for a variable delivery pump having an adjustable swash plate and U.S. Pat. No. 6,216,670 B1 which issued to Michael D. Anderson et al. on Sep. 1, 2001 teaches a somewhat more simplified direct acting control arrangement for a variable delivery pump having an adjustable sleeve arrangement. At times these known variable delivery volume control arrangements are sensitive to changes in oil viscosity. Consequently, when the machine is being started and/or used in cold environments, the response to a needed change in volume may be slower than desired. It is desirable to have a control arrangement that is less susceptible to changes in temperature. The sensitivity of the known control systems to changes in viscosity is many times attributed to large volumes of fluid being passed through small control orifices. Naturally, the thicker the oil the harder it is to force a quantity of oil thereacross in a timely manner.
This invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the subject invention, a variable delivery control arrangement is provided and operative to control the volume of fluid being delivered to a work system. The variable delivery control arrangement includes a fluid pump having an outlet port and a fluid delivery changing mechanism having first and second fluid ports that are operatively associated with the pump. A pressure reducing valve is connected to the outlet port of the pump in parallel with the work system. An infinitely variable control valve arrangement having first and second end portions is disposed in a control conduit between the pressure reducing valve and the second fluid port of the fluid delivery changing mechanism. A first pilot conduit is connected to the control conduit at a point upstream of the infinitely variable control valve arrangement and to both the first port of the fluid delivery changing mechanism and the first end portion of the infinitely variable control valve arrangement. A low pressure conduit is connected to the control conduit between the pressure reducing valve and the infinitely variable control valve and has a flow restrictor and an electrically controlled proportional valve disposed therein. A second pilot conduit is connected between the second end portion of the infinitely variable control valve arrangement and the low pressure conduit at a point between the flow restrictor and the electrically controlled proportional valve.
In another aspect of the subject invention, a method is provided for controlling the delivery of fluid from an outlet port of a pump to a work system. The method includes the steps of connecting a pressure reducing valve to the outlet port of the pump in parallel with the work system; providing a fluid delivery changing mechanism associated with the pump that has first and second fluid ports; connecting the reduced pressure from the pressure reducing valve to the first fluid port of the fluid delivery changing mechanism; positioning an infinitely variable control valve arrangement having first and second end portions between the reduced pressure of the pressure reducing valve and the second fluid port of the fluid delivery changing mechanism to control the flow of reduced pressure fluid to the second fluid port; connecting a low pressure conduit having a flow restrictor therein to the reduced pressure from the pressure reducing valve; positioning an electrically controlled proportional valve in the low pressure conduit downstream of the flow restrictor; and connecting the reduced pressure from the pressure reducing valve to the first end portion of the infinitely variable control valve arrangement and connecting the second end portion thereof to the low pressure conduit between the flow restrictor and the electrically controlled proportional valve.